1. Field of the Invention
This invention relates to automatic slack adjusters of the clearance sensing type for brakes having a running clearance that may be adjusted by controlled rotation of a shaft, such as for example cam actuated brakes, and in particular relates to clearance sensing slack adjusters for cam actuated brakes of the type utilizing a helically wound spring clutch to transfer torque from a driving shaft to a driven shaft which is in driving relation with the actuating cam and/or utilizing a helically wound spring clutch to resist rotation of the driven shaft. More particularly, the invention relates to the surfaces of the shafts around which the spring clutch is wound, at least one of which is provided with a deposit of material different than the material of the remainder of the shaft, such as a deposit of flame sprayed metallic material, to improve the friction and/or wear characteristics of the surface, the improvement comprising providing a shoulder at the end of the shaft bearing the deposit to resist chipping of the deposit and to provide improved retention of the deposit to the shaft.
2. Description of the Prior Art
Automatic slack adjusters of the clearance sensing type for use in connection with cam actuated brakes are known in the prior art. Several of the automatic slack adjusters of the prior art have utilized a drive mechanism defined in part by a helically wound spring clutch wrapped around two abutting shafts to transfer torque in one direction only from a driving shaft to the driven shaft and to slip when the torque required to move the driven shaft exceeded a predetermined limit. Other slack adjusters have utilized a helically wound spring clutch wrapped around one end of a driven shaft and grounded to a housing to resist rotation of the driven shaft relative to the housing in at least one direction of rotation. Examples of such slack adjusters may be seen by reference to U.S. Pat. Nos. 3,507,369 and 3,901,357. It has been found that to obtain proper wear and functional characteristics between the shafts, which are usually of a suitable steel, and the spring clutch, it was desirable to provide a deposit of a different material, such as a flame sprayed molybdenum alloy, on the surface of at least one of the shafts under the spring clutch. In at least one of the prior art slack adjusters, such a deposit was provided on the surface of the end of the driven shaft abutting the driving shaft. The use of such a surface was found to improve the wear and frictional characteristics of that shaft. However, this was not a totally satisfactory arrangement as the deposit of flame sprayed molybdenum alloy was relatively brittle and tended to crack or chip during assembly and/or use which had a negative effect on the performance of the adjuster.